Let be a finite set of integers of cardinality |A|=N⩾2. Given a positive integer k, denote kA (resp. A(k)) the set of all sums (resp. products) of k elements of A. We prove that for all b>1, there exists k=k(b) such that max(|kA|,|A(k)|)>Nb. This answers affirmably questions raised in Erdős and Szemerédi (Stud. Pure Math., 1983, pp. 213–218), Elekes et al. (J. Number Theory 83 (2) (2002) 194–201) and recently, by S. Konjagin (private communication). The method is based on harmonic analysis techniques in the spirit of Chang (Ann. Math. 157 (2003) 939–957) and combinatorics on graphs.
Soit un ensemble fini d'entiers et |A|=N⩾2. Pour tout entier positif k, denotons kA (resp. A(k)) l'ensemble de toutes les sommes (resp. produits) de k éléments de A. On démontre que pour tout b>1, il existe k=k(b) tel que max(|kA|,|A(k)|)>Nb. Ceci répond affirmativement à des questions posées dans Erdős et Szemerédi (Stud. Pure Math., 1983, pp. 213–218), Elekes et al. (J. Number Theory 83 (2) (2002) 194–201) et, récemment, par S. Konjagin (communication privée). La méthode est basée sur des arguments d'analyse harmonique dans l'esprit de Chang (Ann. Math. 157 (2003) 939–957) et de la combinatoire sur des graphes.
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Jean Bourgain 1; Mei-Chu Chang 2
@article{CRMATH_2003__337_8_499_0, author = {Jean Bourgain and Mei-Chu Chang}, title = {On multiple sum and product sets of finite sets of integers}, journal = {Comptes Rendus. Math\'ematique}, pages = {499--503}, publisher = {Elsevier}, volume = {337}, number = {8}, year = {2003}, doi = {10.1016/j.crma.2003.08.010}, language = {en}, }
Jean Bourgain; Mei-Chu Chang. On multiple sum and product sets of finite sets of integers. Comptes Rendus. Mathématique, Volume 337 (2003) no. 8, pp. 499-503. doi : 10.1016/j.crma.2003.08.010. https://comptes-rendus.academie-sciences.fr/mathematique/articles/10.1016/j.crma.2003.08.010/
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